Recently, a technique which realizes a still finer patterning process is more strongly desired for a manufacturing process of a semiconductor integrated circuit to meet a demand for an improvement in precision and a reduction in size. For methods of forming such fine patten, various photo-lithography techniques have been used for practical applications.
For forming a pattern such as wiring, etc., on a semiconductor substrate, the following method is generally adopted. That is, a wiring, etc., is formed by first forming an anti-etching-use mask pattern on a film such as polysilicon film, a metal film, etc., and then carrying out an etching. Here, the photo-lithography process suggests a process of forming a pattern which serves as a mask for etching. For the anti-etching-use mask pattern, a resist (photoconductive resin film) is typically used.
Next, a brief explanation on the method of forming the resist pattern on the semiconductor substrate will be given.
Firstly, while rotating the semiconductor substrate having a wiring-use film, a resist solution is applied onto the semiconductor substrate. Here, as the semiconductor substrate is being rotated, the resist solution can be spread on the entire surface of the semiconductor substrate. As a result, a resist is formed on the semiconductor substrate, thereby forming thereon a resist film.
Secondly, the semiconductor substrate having the resist film is subjected to the exposure process. Here, in an aligner (stepper), a photomask having a predetermined mask pattern (hereinafter referred to as a chrome pattern) consisting of a shielding material such as Cr, etc., is set. In this process of exposure, for the exposure light, it is desirable to use light of a uniform phase having a wavelength of not more than that of the ultraviolet ray. Examples of such desirable light include: i ray (365 nm), KrF eximer laser (248 nm), ArF eximer laser (193 nm), etc.
Lastly, after exposing the semiconductor substrate having formed thereon the resist film, a pre-baking process and a developing process are performed, thereby removing only the area as exposed of the resist film from the semiconductor substrate. As a result, a resist pattern which has the same shape as the mask pattern of the photomask and which is reduced with a predetermined ratio by the reducing projection lens can be formed on the semiconductor substrate.
In the following, explanations on a relationship between (a) the mask pattern of the photomask and (b) the resulting resist pattern to which the mask pattern is transferred will be given in the case of the conventional photo-lithography process of forming a resist pattern having a width substantially equivalent to the wavelength of the exposure light using a positive photoresist in reference to FIG. 5(a) through FIG. 8(b).